The invention relates to a wind energy installation or windmill comprising a wind turbine comprising a rotor and at least one or a plurality of rotor blades. Such wind energy installations are typically installed in regions with high potential of wind energy to increase the amount of electrical energy generated using such wind energy installation. Usually the at least one rotor blade or the plurality of rotor blades are very large and might be tuned e.g. in angle with respect to the direction of the wind and speed of the wind. Therefore the angle of the rotor blades is adjustable with respect to a predetermined direction. In case of very high wind speed the rotor blades are adjustable to reduce the energy produced by the installation or that almost no electrical energy is generated at all. Therefore the risk of damages due to high wind speed might be strongly reduced by the setting of the rotor blades.
Therefore a wind speed measuring system is needed to measure the wind speed and to control the wind energy installation and the pitch of the rotor blades respectively.
EP 0 970 308 B1 discloses a wind speed measuring system which uses a laser anemometry system which uses a laser beam which is directed to particles in the air which itself reflect part of the light of the laser beam and a sensor device is used to measure the light reflected by the laser beam. Since the speed of the particles is almost equal to the speed of the air it is possible to analyse the speed of the particles in order to measure the speed of the air or of the wind. The technique of the system uses an integral measuring method measuring the light reflected from a large amount of particles and therefore the data of the light analysed by the system is an average of the data of the plurality of particles. Accordingly it is not easily achievable to measure the speed of a single particle to determine the speed of the air at a predetermined location or spot at the wind energy installation or in the vicinity of the rotor blades.
Furthermore the measurement equipment and the method are both rather complicated and not adapted to measure the wind speed during the whole operation time of the system.
Furthermore DE 10 2006 041 461 A1 discloses a wind speed measuring system which uses an optical fiber to measure the wind speed. The optical fiber will be heated and due to the wind speed a cooling of the fiber will happen. Therefore the temperature of the fiber is a direct measure of the wind speed at the optical fiber. For detecting the temperature of the optical fiber a fiber Bragg grid (FBG) is used. The fiber Bragg grid technology uses the light reflected within the fiber which is reflected at the Bragg grid itself and the effect that the wave length of the reflected light depends upon the temperature of the spot of the fiber where the fiber Bragg grid is located. The dependency from the temperature stems from the dependency of the optical properties from temperature. Therefore the fiber Bragg grid (FBG) allows indirectly the measurement of the wind speed at a predetermined spot of the fiber due to the indirect measurement of the temperature of the fiber.
The above mentioned technology has the striking drawback that the optical fiber has to be heated all the time at a very constant temperature in order to measure the wind speed with an expected degree of accuracy. The heating of the fiber consumes electrical energy and is this energy consumption is therefore strongly inefficient and not acceptable for a standard use during extended time periods. In case of a use only from time to time including periods of time without wind speed measurement the wind energy installation reveals a great disadvantage with regard to safety of the installation itself.